Methods and apparatus for symmetrical hollow cathode electrode and discharge mode for remote plasma processes

ABSTRACT

Methods and apparatus for reducing particle generation in a remote plasma source (RPS) include an RPS having a first plasma source with a first electrode and a second electrode, wherein the first electrode and the second electrode are symmetrical with hollow cavities configured to induce a hollow cathode effect within the hollow cavities, and wherein the RPS provides radicals or ions into the processing volume, and a radio frequency (RF) power source configured to provide a symmetrical driving waveform on the first electrode and the second electrode to produce an anodic cycle and a cathodic cycle of the RPS, wherein the anodic cycle and the cathodic cycle operate in a hollow cathode effect mode.

FIELD

Embodiments of the present principles generally relate to semiconductorchambers used in semiconductor processes.

BACKGROUND

Some process chambers may include a remote plasma source (RPS) forforming plasma remotely from a process chamber into which the radicalsand/or ionized species are to be delivered. Conventionally, the RPS isconnected to the processing chamber through a mixing reservoir formixing a process gas stream provided by the RPS with a dilutant (orcarrier) gas or other fluids prior to delivery to the chamber. Ions orradicals may then be dispersed into a processing volume of the processchamber to perform processes such as etching or cleaning. An RPS mayinclude an RF electrode with a hollow cavity and a ground electrodeconsisting of a flat grounding plate. The RF electrode with the hollowcavity creates a hollow cathode mode that enhances electron impactionization within the hollow cavity. The ground electrode with the flatgrounding plate produces a glow discharge mode. The inventors haveobserved that if a sinusoidal driving system is used for such an RPS,particles may be produced during the glow discharge mode that causedefects on the wafers being processed.

Thus, the inventors have provided improved methods and apparatus toproduce remote plasma without generating particles.

SUMMARY

Methods and apparatus for reduction of particle generation during remoteplasma generation are provided herein.

In some embodiments, an apparatus for processing a substrate maycomprise a process chamber with a chamber body enclosing a processingvolume, a remote plasma source (RPS) having a first plasma source with afirst electrode and a second electrode, wherein the first electrode andthe second electrode are symmetrical with hollow cavities configured toinduce a hollow cathode effect within the hollow cavities, and whereinthe RPS provides radicals or ions into the processing volume and a radiofrequency (RF) power source configured to provide a symmetrical drivingwaveform on the first electrode and the second electrode to produce ananodic cycle and a cathodic cycle of the RPS, wherein the anodic cycleand the cathodic cycle operate in a hollow cathode effect mode.

In some embodiments, the apparatus may further comprise wherein thesymmetrical driving waveform is a sinusoidal waveform or a square wavewaveform, an isolator between the first electrode and the secondelectrode, wherein the isolator has a ring shape, wherein the isolatorhas at least one groove on a radially inward side of the ring shape thatis configured to be exposed to generated plasma from the first electrodeand the second electrode, wherein the isolator is formed of a ceramicmaterial, wherein the first electrode and the second electrode havehollow cavities with a cone shape having a first end with a firstdiameter opening and a second end with a second diameter opening,wherein the second diameter opening is larger than the first diameteropening, wherein the second diameter opening of the first electrode isconfigured to face the second diameter opening of the second electrode,a mixing reservoir located between the first plasma source and theprocessing volume, a second plasma source with a third electrode and afourth electrode, wherein the third electrode and the fourth electrodeare symmetrical with hollow cavities configured to induce a hollowcathode effect within the hollow cavities, and/or wherein the firstplasma source and the second plasma source provide radicals or ions intoa mixing reservoir that is fluidly connected to the processing volume.

In some embodiments, an apparatus for processing a substrate maycomprise a remote plasma source (RPS) having a first plasma source witha first electrode and a second electrode, wherein the first electrodeand the second electrode are symmetrical with hollow cavities configuredto induce a hollow cathode effect within the hollow cavities and a radiofrequency (RF) power source configured to provide a symmetrical drivingwaveform on the first electrode and the second electrode to produce ananodic cycle and a cathodic cycle of the RPS, wherein the anodic cycleand the cathodic cycle operate in a hollow cathode effect mode.

In some embodiments, the apparatus may further comprise whereinsymmetrical driving waveform is a sinusoidal waveform or a square wavewaveform, an isolator between the first electrode and the secondelectrode, wherein the isolator has a ring shape and is formed of aceramic based material, and wherein the isolator has at least one grooveon a radially inward side of the ring shape that is configured to beexposed to generated plasma from the first electrode and the secondelectrode, wherein the first electrode and the second electrode havehollow cavities with a cone shape having a first end with a firstdiameter opening and a second end with a second diameter opening,wherein the second diameter opening is larger than the first diameteropening, wherein the second diameter opening of the first electrode isconfigured to face the second diameter opening of the second electrode,and/or a second plasma source with a third electrode and a fourthelectrode, wherein the third electrode and the fourth electrode aresymmetrical with hollow cavities configured to induce a hollow cathodeeffect within the hollow cavities, and wherein the first plasma sourceand the second plasma source provide radicals or ions into a mixingreservoir that is fluidly connected to a processing volume of a processchamber.

In some embodiments, a method of generating remote plasma for a processchamber may comprise generating a symmetrical driving waveform with aradio frequency (RF) power source for a first plasma source and formingplasma in the first plasma source by applying the symmetrical drivingwaveform to a first electrode and to a second electrode of the firstplasma source, wherein the first electrode and the second electrode aresymmetrical with hollow cavities configured to induce a hollow cathodeeffect within the hollow cavities when driven by the symmetrical drivingwaveform.

In some embodiments, the method may further comprise forming plasma in asecond plasma source by applying the symmetrical driving waveform to athird electrode and to a fourth electrode of the second plasma source,wherein the third electrode and the fourth electrode are symmetricalwith hollow cavities configured to induce a hollow cathode effect withinthe hollow cavities when driven by the symmetrical driving waveform,and/or mixing radicals or ions generated by the first plasma source andthe second plasma source in a mixing reservoir that is fluidly coupledto a processing volume of a process chamber.

Other and further embodiments are disclosed below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present principles, briefly summarized above anddiscussed in greater detail below, can be understood by reference to theillustrative embodiments of the principles depicted in the appendeddrawings. However, the appended drawings illustrate only typicalembodiments of the principles and are thus not to be considered limitingof scope, for the principles may admit to other equally effectiveembodiments.

FIG. 1 depicts a schematic cross-sectional view of a process chamberwith a remote plasma source in accordance with some embodiments of thepresent principles.

FIG. 2 depicts a schematic cross-sectional view of a plasma source withsymmetric electrodes in accordance with some embodiments of the presentprinciples.

FIG. 3 depicts a schematic cross-sectional view of a plasma source withsymmetric electrodes and an isolator in accordance with some embodimentsof the present principles.

FIG. 4 depicts an isometric view of an isolator in accordance with someembodiments of the present principles.

FIG. 5 depicts a schematic cross-sectional view of a remote plasmasource with multiple plasma sources with symmetric electrodes inaccordance with some embodiments of the present principles.

FIG. 6 depicts a schematic cross-sectional view of a remote plasmasource with multiple plasma sources in accordance with some embodimentsof the present principles.

FIG. 7 is a method of remotely generating plasma for a process chamberin accordance with some embodiments of the present principles.

FIG. 8 depicts a graph of a symmetric driving waveform in accordancewith some embodiments of the present principles.

FIG. 9 depicts a hollow cathode effect cavity in accordance with someembodiments of the present principles.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. Elements and features of one embodiment may be beneficiallyincorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

The methods and apparatus provide an improved remote plasma source (RPS)with symmetrical hollow electrodes that produce hollow cathode effectmodes for anodic and cathodic cycles of a symmetrical RF drive system.The improved RPS eliminates the glow discharge mode for anodic cyclesfound in typical RPS systems which causes particle generation in theprocess chamber, leading to wafer defects and lower wafer output. Themethods and apparatus of the present principles use a symmetricalelectrode configuration along with a symmetrical driving voltagewaveform to generate the hollow cathode discharge modes. The symmetricalelectrode and driving configuration enables higher power to be usedwithout particle generation and increases throughput. In addition,elimination of the glow discharge mode increases the lifetime of the RFsystem by preventing a buildup on an isolator used between theelectrodes. The symmetrical hollow cavity electrodes may be used with RFpower systems with symmetrical driving waveforms with frequenciesranging from 10's of kilohertz to 100's of kilohertz to enable a hollowcathode effect mode for both the cathodic and the anodic cycles. Theinventors found that the symmetrical waveform has the benefit ofneutralizing charged particles that accumulate in a previous cycle. Asymmetrical waveform may include, but is not limited to, a sinusoidalwaveform or a square wave waveform and the like.

Some process chambers have an asymmetrical electrode configuration thatgives two different discharge modes consisting of a hollow cathode modeand a glow discharge mode for cathodic and anodic cycles. The inventorshave found that the glow discharge mode causes particles to be generatedfrom sputtering of the electrodes due to high energy ion bombardment.The generated particles may fall on a wafer and affect the performanceof the semiconductor. Particle performance was found to be even worsefor higher RF power, seriously limiting the throughput as the RF powermust be reduced to increase particle performance and reduce particlegeneration.

The methods and apparatus may be used for different types of processchambers such as preclean chambers or etch chambers and the like. As anexample chamber use, FIG. 1 depicts a cross-sectional view of a processchamber 100 with a remote plasma source 164 in accordance with someembodiments. The process chamber 100 is a vacuum chamber which isadapted to maintain sub-atmospheric pressures within an interior volume102 during substrate processing. In some embodiments, the processchamber 100 can maintain a pressure of approximately 1 mTorr to 100Torr. The process chamber 100 includes a chamber body 104 which enclosesa processing volume 108 located in the upper half of the interior volume102. The chamber body 104 may be made of metal, such as aluminum and thelike. The chamber body 104 may be grounded via a coupling to ground 110.

A substrate support 112 is disposed within the interior volume 102 tosupport and retain a substrate 114, such as a semiconductor wafer, forexample, or other such substrate. The substrate support 112 maygenerally comprise a pedestal 116 and a hollow support shaft 118 forsupporting the pedestal 116. The pedestal 116 may be composed of analuminum-based material or a ceramic-based material and the like. Apedestal formed of a ceramic-based material may be used for hightemperature processes. The hollow support shaft 118 provides a conduitto provide, for example, backside gases, process gases, fluids,coolants, power, or the like, to the pedestal 116. In some embodiments,the substrate support 112 includes a focus ring 120 disposed about thepedestal 116 to enhance process uniformity at an edge of the substrate114. In some embodiments, the focus ring 120 is made of quartz-basedmaterials. In some embodiments, the focus ring 120 is made ofceramic-based materials. The ceramic-based material facilitates highpressure process capabilities. A slit valve 122 may be coupled to thechamber body 104 to facilitate in transferring the substrate 114 intoand out of the interior volume 102.

In some embodiments, the hollow support shaft 118 is coupled to a liftactuator 124, such as a motor, which provides vertical movement of thepedestal 116 between an upper, processing position, and a lower,transfer position. A substrate lift 126 can include lift pins 128mounted on a platform 130 connected to a shaft 132 which is coupled to asecond lift actuator 134 for raising and lowering the substrate lift 126so that the substrate 114 may be placed on or removed from the pedestal116. The pedestal 116 may include through-holes to receive the lift pins128. The hollow support shaft 118 provides a path for a gas conduit 194for coupling a backside gas supply 136 and/or an RF power supply 138 tothe pedestal 116. In some embodiments, the RF power supply 138 providesbias power through a matching network 140 to a power conduit 142 to thepedestal 116. In some embodiments, RF energy supplied by the RF powersupply 138 may have a frequency of about 2 MHz or greater. In someembodiments, the RF power supply 138 may have a frequency of about 13.56MHz.

In some embodiments, the backside gas supply 136 is disposed outside ofthe chamber body 104 and supplies gas to the pedestal 116. In someembodiments, the pedestal 116 includes a gas channel 144, allowing gasto interact with a backside of the substrate 114 to maintain a giventemperature. The gas channel 144 is configured to provide backside gas,such as nitrogen (N), argon (Ar), or helium (He), to an upper surface146 of the pedestal 116 to act as a heat transfer medium. The gaschannel 144 is in fluid communication with the backside gas supply 136via gas conduit 194 to control the temperature and/or temperatureprofile of the substrate 114 during use. For example, the backside gassupply 136 can supply gas to cool and/or heat the substrate 114 duringuse. In some embodiments, the substrate 114 may be heated fromapproximately 60 degrees Celsius to approximately 450 degrees Celsius.

The process chamber 100 includes a process kit circumscribing variouschamber components to prevent unwanted reaction between such componentsand contaminants. The process kit includes an upper shield 148. In someembodiments, the upper shield 148 may be made of metal, such asaluminum. In some embodiments, the process kit may be constructed ofquartz. In some embodiments, a mixing reservoir 156 is coupled to and influid communication with the processing volume 108. The mixing reservoir156 is also fluidly connected to the RPS 164. The mixing reservoir 156allows mixing of the plasma gases with other gases provided by a gasdelivery system 150. A rate of flow of the other gases from the gasdelivery system 150 may be controlled by a first flow valve 188.

A showerhead 158 is located above the processing volume 108 and below aceiling 162 of the chamber body 104. The showerhead 158 includesthrough-holes 160 to flow gases from the mixing reservoir 156 into theprocessing volume 108. The RPS 164 is fluidly connected to the mixingreservoir 156 to allow ionized gases to flow from the RPS 164 into themixing reservoir 156, through the showerhead 158, and into theprocessing volume 108. Plasma is generated in the RPS 164 by a plasma RFpower source 166 that provides RF energy to the RPS 164. Process gasesused to form the plasma are supplied by a process gas source 170 andcontrolled by a second flow valve 186. The plasma gases supplied by theprocess gas source 170 may include, but are not limited to, hydrogen,helium, and/or argon and the like. The RPS 164 produces ions andradicals of the process gas to facilitate in processing the substrate114.

A pump port 172 is configured to facilitate removal of particles andgases from the interior volume 102. The process chamber 100 is coupledto and in fluid communication with a vacuum system 174 which includes athrottle valve (not shown) and pump (not shown) which are used toexhaust the process chamber 100. In some embodiments, the vacuum system174 is coupled to the pump port 172 disposed on a bottom surface 176 ofthe chamber body 104. The pressure inside the process chamber 100 may beregulated by adjusting the throttle valve and/or vacuum pump. In someembodiments, the pump has a flow rate of approximately 1900 liters persecond to approximately 3000 liters per second. In some embodiments, thevacuum system 174 may be used to facilitate in regulating the substratetemperature.

In some embodiments, a controller 178 is used for the operation of theprocess chamber 100. The controller 178 may use direct control of theprocess chamber 100 or alternatively, use indirect control of theprocess chamber 100 by controlling computers (or controllers) associatedwith the process chamber 100. In operation, the controller 178 enablesdata collection and feedback from the process chamber 100 to optimizeperformance of the process chamber 100. The controller 178 generallyincludes a Central Processing Unit (CPU) 180, a memory 182, and asupport circuit 184. The CPU 180 may be any form of a general-purposecomputer processor that can be used in an industrial setting. Thesupport circuit 184 is conventionally coupled to the CPU 180 and maycomprise a cache, clock circuits, input/output subsystems, powersupplies, and the like. Software routines, such as a method as describedbelow may be stored in the memory 182 and, when executed by the CPU 180,transform the CPU 180 into a specific purpose computer (controller 178).The software routines may also be stored and/or executed by a secondcontroller (not shown) that is located remotely from the process chamber100.

The memory 182 is in the form of computer-readable storage media thatcontains instructions, when executed by the CPU 180, to facilitate theoperation of the semiconductor processes and equipment. The instructionsin the memory 182 are in the form of a program product such as a programthat implements the method of the present principles. The program codemay conform to any one of a number of different programming languages.In one example, the disclosure may be implemented as a program productstored on a computer-readable storage media for use with a computersystem. The program(s) of the program product define functions of theaspects (including the methods described herein). Illustrativecomputer-readable storage media include, but are not limited to:non-writable storage media (e.g., read-only memory devices within acomputer such as CD-ROM disks readable by a CD-ROM drive, flash memory,ROM chips, or any type of solid-state non-volatile semiconductor memory)on which information is permanently stored; and writable storage media(e.g., floppy disks within a diskette drive or hard-disk drive or anytype of solid-state random access semiconductor memory) on whichalterable information is stored. Such computer-readable storage media,when carrying computer-readable instructions that direct the functionsof the methods described herein, are aspects of the present principles.

FIG. 2 depicts a cross-sectional view of a plasma source 200 with anupper symmetric electrode 202A and a lower symmetric electrode 202B inaccordance with some embodiments. During operation of the RPS 164, gasenters a gas port 210 and plasma related products exit through adiffuser hole 208 into the mixing reservoir 156. The diffuser hole 208may have a diameter of approximately 0.1 inches to approximately 0.2inches. The upper symmetric electrode 202A and the lower symmetricelectrode 202B have a respective upper symmetric cavity 204A and arespective lower symmetric cavity 204B that are configured to produce ahollow cathode effect. The upper symmetric electrode 202A and the lowersymmetric electrode 202B are separated by a gap 206. The gap 206 mayseparate the upper symmetric electrode 202A and the lower symmetricelectrode 202B by a distance of approximately 0.2 inches toapproximately 0.5 inches. The upper symmetric cavity 204A and the lowersymmetric cavity 204B have a cone shape 902 as illustrated in theisometric view of FIG. 9. FIG. 9 depicts a hollow cathode effect cavity900 in accordance with some embodiments.

In FIG. 9, the cone shape 902 has a vertical axis 904 in a center. At afirst end 910 is an opening to fluidly connect with a gas supply (e.g.,process gas source 170). The opening at the first end 910 may have adiameter of approximately 0.1 inches to approximately 0.2 inches. At asecond end 912 is a larger flared opening that fluidly connects with thegap 206 between the upper symmetric electrode 202A and the lowersymmetric electrode 202B. In some embodiments, the cone shape 902 mayhave a first cone section 914 with a first angle 906 of approximately 10degrees to approximately 30 degrees. In some embodiments, the cone shape902 may a second cone section 916 that has a larger flared opening witha second angle 908 of approximately 10 degrees to approximately 60degrees. In some embodiments, a height 918 of the cone shape 902 may beapproximately 1.5 inches to approximately 2 inches.

The plasma RF power source 166 produces a symmetric driving waveform 802(e.g., a sinusoidal waveform is shown as a non-limiting example) asillustrated in a graph 800 of FIG. 8. During a cathodic period 806, ahollow cathode mode caused by the upper symmetric cavity 204A formsplasma 212. During an anodic period 804, a hollow cathode mode caused bythe lower symmetric cavity 204B forms plasma 212. In conventionalsystems with a grounding plate for the lower electrode, the anodicperiod 804 would instead produce a glow discharge mode due to thegrounding plate, generating particles that would be detrimental tosemiconductor performance. With the upper symmetric electrode 202A andthe lower symmetric electrode 202B of the present principles, theparticle performance is substantially increased. During testing, theinventors found that when the upper symmetric cavity 204A and the lowersymmetric cavity 204B are configured to produce a hollow cathode effect,the RPS 164 had superior particle performance compared to an RPS withparallel flat plane electrodes that produced a glow discharge for boththe anodic and cathodic periods of the symmetric driving waveform 802.

During other testing, the inventors found that when a top electrode witha hollow cavity and a bottom electrode that is a plate electrode is usedas ground (i.e., “asymmetrical electrodes”), two different plasma modeswere generated when the plasma source was driven with a symmetricalwaveform. During the anodic period 804, a thin plasma is formed right ontop of the plate electrode used as the ground. During the cathodicperiod 806, a strong hollow cathode effect occurs at the center of thehollow cavity of the top electrode forming plasma at the center (“hollowcathode effect”). The inventors found that the hollow cathode modeimproved etch performance. When the driving waveform was changed suchthat only cathodic periods were present (half sinusoidal waveform), theinventors found an improved etch performance but also found a negativeside effect of a buildup of material within the gap separating the topand bottom electrodes of the plasma source.

When the electrodes were changed to parallel flat electrodes with a gapbetween, a glow discharge mode was created for both anodic and cathodicperiods, resulting in a decrease of etch performance and generation of asubstantial number of particles. The inventors discovered that usingsymmetric electrodes with hollow cavities configured to create hollowcathode effect modes for anodic and cathodic periods improved the etchperformance substantially over a single cone shaped hollow electrode. Insome embodiments, a ceramic ring (see FIG. 3 below) is used to furtherreduce the glow discharge mode in the gap 206 where the electrodes formparallel surfaces 220 (away from the cone shaped cavities). In someembodiments, a ceramic coating 222 at least on one of the parallelsurfaces 220 (top parallel surface 220A of bottom electrode or bottomparallel surface 220B of top electrode) is used to further reduce theglow discharge mode in the gap 206 where the electrodes form parallelsurfaces 220 (away from the cone shaped cavities).

FIG. 3 depicts a cross-sectional view of a plasma source 300 with anoptional isolator 302 between the upper symmetric electrode 202A and thelower symmetric electrode 202B in accordance with some embodiments. Theinventors found that using an optional isolator 302 in the gap 206facilitates in reducing particle buildup on surfaces of the gap 206 byreducing electric fields between the upper symmetric electrode 202A andthe lower symmetric electrode 202B. In some embodiments, the optionalisolator 302 may be ring shaped and formed from a ceramic-basedmaterial. An optional groove 304 may be formed into an interior surface402 of the optional isolator 302 to increase surface area on theinterior of the optional isolator 302. In some embodiments, more thanone optional groove 304 may be formed into the interior surface 402 ofthe optional isolator 302. In some instances, nickel buildup may occuron the interior surface 402 of the optional isolator 302. The additionof the optional groove 304 increases the surface area of the interiorsurface 402 reducing electrical arcing through the nickel buildup andavoiding electrical discharge between the upper symmetric electrode 202Aand the lower symmetric electrode 202B. FIG. 4 depicts an isometric view400 of the optional isolator 302 in accordance with some embodiments.The interior surface 402 may also have one or more optional grooves (notshown, see FIG. 3).

The parallel surfaces 220 of the gap 206 have a very strong electricfield strength compared to the hollow cavities during operation. Thestrong electric field strength causes high ion energies which forces theions to repeatedly strike the parallel surfaces 220, sputtering materialfrom the electrode surfaces. In some embodiments, the electrodes areformed of or coated with a nickel-based material which is then sputteredby the high energy ions in the parallel surface regions of the gap. Thesputtering may cause nickel particles or nickel buildup due to the ionbombardment. The sputtering may be reduced or eliminated by reducing theelectric fields through the use of the optional isolator 302 or ceramiccoating 222. The inventors found that by reducing the electric fields inthe parallel surface regions of the gap, more current will flow throughthe hollow cavity regions and amplify the hollow cathode effect of thehollow cavities, substantially increasing the etch performance. Forexample, the inventors found that using symmetrical electrodes mayincrease the etch rate by approximately 20 percent to approximately 40percent. By reducing the electric fields in the parallel surface regionsof the gap 206, the inventors found that the etch rate may be increasedby 500 percent or more.

FIG. 5 depicts a cross-sectional view of a remote plasma source 500 withmultiple plasma sources 164A, 164B with symmetric electrodes inaccordance with some embodiments. Throughput may be increased by usingtwo or more plasma sources in the RPS 500. In some embodiments, themultiple plasma sources 164A, 164B are mounted to a dome ceiling 502 ofa mixing reservoir 156A. The dome ceiling 502 allows the multiple plasmasources 164A, 164B to be mounted at an angle that permits connection ofmultiple units that feed the mixing reservoir 156A. A plasma RF powersystem 504 may have one or more plasma RF power supplies 506A, 506Bwhich may provide power independently or in conjunction as determined bypower controller 508. FIG. 6 depicts a cross-sectional view of a remoteplasma source 600 with multiple plasma sources 602A, 602B in accordancewith some embodiments. Throughput is increased but without the benefitsof having symmetric electrodes.

FIG. 7 is a method 700 of remotely generating plasma for a processchamber in accordance with some embodiments. In block 702, a symmetricaldriving waveform is generated by an RF power source for a first plasmasource in an RPS. In some embodiments, the symmetrical driving waveformmay be a sinusoidal waveform or a square wave waveform and the like. Thesymmetrical waveform has the benefit of neutralizing charged particlesthat accumulate in a previous cycle. In block 704, plasma is formed inthe first plasma source by applying the symmetrical driving waveform toa first electrode and to a second electrode of the first plasma source.The first electrode and the second electrode are symmetrical and havehollow cavities that are configured to induce a hollow cathode effectwithin the hollow cavities when driven by the symmetrical drivingwaveform. In some embodiments, the ions and/or radicals from the plasmaflows into a mixing reservoir where additional gases may be mixed in.The resulting mixture then flows into a processing volume of a processchamber to process a substrate.

In some embodiments, more than one plasma source may be used. Althoughexamples herein may illustrate two plasma sources for brevity, anynumber of plasma sources may be used. In optional block 706, plasma isformed in a second plasma source by applying the symmetrical drivingwaveform to a third electrode and to a fourth electrode of the secondplasma source. The third electrode and the fourth electrode aresymmetrical and have hollow cavities configured to induce a hollowcathode effect within the hollow cavities when driven by the symmetricaldriving waveform. In optional block 708, radicals or ions generated bythe first plasma source and the second plasma source are mixed in amixing reservoir that is fluidly coupled to a processing volume of aprocess chamber. The mixing of the two plasma sources allows an RPS toincrease throughput and/or ion/radical density.

Embodiments in accordance with the present principles may be implementedin hardware, firmware, software, or any combination thereof. Embodimentsmay also be implemented as instructions stored using one or morecomputer readable media, which may be read and executed by one or moreprocessors. A computer readable medium may include any mechanism forstoring or transmitting information in a form readable by a machine(e.g., a computing platform or a “virtual machine” running on one ormore computing platforms). For example, a computer readable medium mayinclude any suitable form of volatile or non-volatile memory. In someembodiments, the computer readable media may include a non-transitorycomputer readable medium.

While the foregoing is directed to embodiments of the presentprinciples, other and further embodiments of the principles may bedevised without departing from the basic scope thereof.

The invention claimed is:
 1. An apparatus for processing a substrate,comprising: a process chamber with a chamber body enclosing a processingvolume; a remote plasma source (RPS) having a first plasma source with afirst electrode and a second electrode, wherein the first electrode andthe second electrode are symmetrical with hollow cavities configured toinduce a hollow cathode effect within the hollow cavities, and whereinthe RPS is configured to provide radicals or ions into the processingvolume; and a radio frequency (RF) power source configured to provide asymmetrical driving waveform on the first electrode and the secondelectrode to produce an anodic cycle and a cathodic cycle of the RPS,wherein the anodic cycle and the cathodic cycle operate in a hollowcathode effect mode; and an isolator between the first electrode and thesecond electrode, wherein the isolator has a ring shape and has at leastone groove on a radially inward side of the ring shape that isconfigured to be exposed to generated plasma from the first electrodeand the second electrode.
 2. The apparatus of claim 1, wherein thesymmetrical driving waveform is a sinusoidal waveform or a square wavewaveform.
 3. The apparatus of claim 1, wherein the isolator is formed ofa ceramic material.
 4. The apparatus of claim 1, wherein the firstelectrode and the second electrode have hollow cavities with a coneshape having a first end with a first diameter opening and a second endwith a second diameter opening, wherein the second diameter opening islarger than the first diameter opening.
 5. The apparatus of claim 4,wherein the second diameter opening of the first electrode is configuredto face the second diameter opening of the second electrode.
 6. Theapparatus of claim 1, further comprising: a mixing reservoir locatedbetween the first plasma source and the processing volume.
 7. Theapparatus of claim 1, further comprising: a second plasma source with athird electrode and a fourth electrode, wherein the third electrode andthe fourth electrode are symmetrical with hollow cavities configured toinduce a hollow cathode effect within the hollow cavities.
 8. Theapparatus of claim 7, wherein the first plasma source and the secondplasma source provide radicals or ions into a mixing reservoir that isfluidly connected to the processing volume.
 9. An apparatus forprocessing a substrate, comprising: a remote plasma source (RPS) havinga first plasma source with a first electrode and a second electrode,wherein the first electrode and the second electrode are symmetricalwith hollow cavities configured to induce a hollow cathode effect withinthe hollow cavities; and a radio frequency (RF) power source configuredto provide a symmetrical driving waveform on the first electrode and thesecond electrode to produce an anodic cycle and a cathodic cycle of theRPS, wherein the anodic cycle and the cathodic cycle operate in a hollowcathode effect mode; and an isolator between the first electrode and thesecond electrode, wherein the isolator has a ring shape and has at leastone groove on a radially inward side of the ring shape that isconfigured to be exposed to generated plasma from the first electrodeand the second electrode.
 10. The apparatus of claim 9, whereinsymmetrical driving waveform is a sinusoidal waveform or a square wavewaveform.
 11. The apparatus of claim 9, further comprising: wherein theisolator is formed of a ceramic based material.
 12. The apparatus ofclaim 9, wherein the first electrode and the second electrode havehollow cavities with a cone shape having a first end with a firstdiameter opening and a second end with a second diameter opening,wherein the second diameter opening is larger than the first diameteropening.
 13. The apparatus of claim 12, wherein the second diameteropening of the first electrode is configured to face the second diameteropening of the second electrode.
 14. The apparatus of claim 9, furthercomprising: a second plasma source with a third electrode and a fourthelectrode, wherein the third electrode and the fourth electrode aresymmetrical with hollow cavities configured to induce a hollow cathodeeffect within the hollow cavities, and wherein the first plasma sourceand the second plasma source provide radicals or ions into a mixingreservoir that is fluidly connected to a processing volume of a processchamber.
 15. A method of generating remote plasma for a process chamber,comprising: generating a symmetrical driving waveform with a radiofrequency (RF) power source for a first plasma source; and formingplasma in the first plasma source by applying the symmetrical drivingwaveform to a first electrode and to a second electrode of the firstplasma source with an isolator between the first electrode and thesecond electrode, wherein the first electrode and the second electrodeare symmetrical with hollow cavities configured to induce a hollowcathode effect within the hollow cavities when driven by the symmetricaldriving waveform and wherein the isolator has a ring shape and has atleast one groove on a radially inward side of the ring shape that isconfigured to be exposed to generated plasma from the first electrodeand the second electrode.
 16. The method of claim 15, furthercomprising: forming plasma in a second plasma source by applying thesymmetrical driving waveform to a third electrode and to a fourthelectrode of the second plasma source, wherein the third electrode andthe fourth electrode are symmetrical with hollow cavities configured toinduce a hollow cathode effect within the hollow cavities when driven bythe symmetrical driving waveform.
 17. The method of claim 16, furthercomprising: mixing radicals or ions generated by the first plasma sourceand the second plasma source in a mixing reservoir that is fluidlycoupled to a processing volume of a process chamber.